diff --git a/src/opm/output/eclipse/Summary.cpp b/src/opm/output/eclipse/Summary.cpp
index 89d899b28..5eab20b0f 100644
--- a/src/opm/output/eclipse/Summary.cpp
+++ b/src/opm/output/eclipse/Summary.cpp
@@ -1577,6 +1577,73 @@ quantity well_guiderate(const fn_args& args)
     return guiderate_value<i>(xwPos->second.guide_rates);
 }
 
+quantity well_efficiency_factor(const fn_args& args)
+{
+    const auto zero = quantity { 0.0, measure::identity };
+
+    if (args.schedule_wells.empty()) {
+        return zero;
+    }
+
+    const auto* well = args.schedule_wells.front();
+
+    auto xwPos = args.wells.find(well->name());
+    if ((xwPos == args.wells.end()) ||
+        (xwPos->second.dynamicStatus == Opm::Well::Status::SHUT))
+    {
+        // Non-flowing wells have a zero efficiency factor
+        return zero;
+    }
+
+    return { well->getEfficiencyFactor(), measure::identity };
+}
+
+quantity well_efficiency_factor_grouptree(const fn_args& args)
+{
+    const auto zero = quantity { 0.0, measure::identity };
+
+    if (args.schedule_wells.empty()) {
+        return zero;
+    }
+
+    const auto* well = args.schedule_wells.front();
+
+    auto xwPos = args.wells.find(well->name());
+    if ((xwPos == args.wells.end()) ||
+        (xwPos->second.dynamicStatus == Opm::Well::Status::SHUT))
+    {
+        // Non-flowing wells have a zero efficiency factor
+        return zero;
+    }
+
+    auto factor = well->getEfficiencyFactor();
+    auto parent = well->groupName();
+    while (parent != "FIELD") {
+        const auto& grp = args.schedule[args.sim_step].groups(parent);
+        factor *= grp.getGroupEfficiencyFactor();
+
+        const auto prnt = grp.control_group();
+        parent = prnt.has_value() ? prnt.value() : "FIELD";
+    }
+
+    return { factor, measure::identity };
+}
+
+quantity group_efficiency_factor(const fn_args& args)
+{
+    const auto zero = quantity { 0.0, measure::identity };
+
+    if (args.schedule_wells.empty()) {
+        return zero;
+    }
+
+    const auto gefac =
+        args.schedule[args.sim_step].groups(args.group_name)
+        .getGroupEfficiencyFactor();
+
+    return { gefac, measure::identity };
+}
+
 /*
  * A small DSL, really poor man's function composition, to avoid massive
  * repetition when declaring the handlers for each individual keyword. bin_op
@@ -2117,6 +2184,11 @@ static const std::unordered_map< std::string, ofun > funs = {
     { "WGPI", potential_rate< rt::well_potential_gas , false, true>},
     { "WGIP", potential_rate< rt::well_potential_gas , false, true>}, // Alias for 'WGPI'
     { "ROEW", roew },
+
+    // Efficiency factors
+    {"GEFF" , group_efficiency_factor},
+    {"WEFF" , well_efficiency_factor},
+    {"WEFFG", well_efficiency_factor_grouptree},
 };
 
 static const std::unordered_map< std::string, Opm::UnitSystem::measure> single_values_units = {
diff --git a/tests/SUMMARY_EFF_FAC.DATA b/tests/SUMMARY_EFF_FAC.DATA
index 8bb49df1b..7e03363cb 100644
--- a/tests/SUMMARY_EFF_FAC.DATA
+++ b/tests/SUMMARY_EFF_FAC.DATA
@@ -74,6 +74,10 @@ WOIR
 /
 WOIT
 /
+WEFF
+/
+WEFFG
+/
 
 GOPR
 /
@@ -98,6 +102,8 @@ GGPI
 /
 GWPI
 /
+GEFF
+/
 
 FOPR
 
diff --git a/tests/test_Summary.cpp b/tests/test_Summary.cpp
index e95c1413f..ead12b68e 100644
--- a/tests/test_Summary.cpp
+++ b/tests/test_Summary.cpp
@@ -2293,6 +2293,12 @@ BOOST_AUTO_TEST_CASE(efficiency_factor) {
         BOOST_CHECK_CLOSE( 10.1, ecl_sum_get_well_var( resp, 1, "W_1", "WOPT" ), 1e-5 );
         BOOST_CHECK_CLOSE( 2 * 10.1, ecl_sum_get_well_var( resp, 2, "W_1", "WOPT" ), 1e-5 );
 
+        BOOST_CHECK_CLOSE( 1.0, ecl_sum_get_well_var( resp, 1, "W_1", "WEFF" ), 1.0e-5 );
+        BOOST_CHECK_CLOSE( 1.0, ecl_sum_get_well_var( resp, 2, "W_1", "WEFF" ), 1.0e-5 );
+
+        BOOST_CHECK_CLOSE( 1.0, ecl_sum_get_well_var( resp, 1, "W_1", "WEFFG" ), 1.0e-5 );
+        BOOST_CHECK_CLOSE( 1.0, ecl_sum_get_well_var( resp, 2, "W_1", "WEFFG" ), 1.0e-5 );
+
         BOOST_CHECK_CLOSE( 10.1, ecl_sum_get_well_var( resp, 1, "W_1", "WOPR" ), 1e-5 );
         BOOST_CHECK_CLOSE( 10.1, ecl_sum_get_well_var( resp, 1, "W_1", "WOPT" ), 1e-5 );
         BOOST_CHECK_CLOSE( 2 * 10.1, ecl_sum_get_well_var( resp, 2, "W_1", "WOPT" ), 1e-5 );
@@ -2309,6 +2315,9 @@ BOOST_AUTO_TEST_CASE(efficiency_factor) {
         BOOST_CHECK_CLOSE(   0.0 , ecl_sum_get_group_var( resp, 2, "G_1", "GWPI" ), 1e-5 );
         BOOST_CHECK_CLOSE(   0.0 , ecl_sum_get_group_var( resp, 2, "G_1", "GGPI" ), 1e-5 );
 
+        BOOST_CHECK_CLOSE( 1.0, ecl_sum_get_group_var( resp, 1, "G_1", "GEFF" ), 1.0e-5 );
+        BOOST_CHECK_CLOSE( 1.0, ecl_sum_get_group_var( resp, 2, "G_1", "GEFF" ), 1.0e-5 );
+
         /* WEFAC 0.2 assigned to W_2.
          * W_2 assigned to group G2. GEFAC G2 = 0.01 */
         BOOST_CHECK_CLOSE( 20.1, ecl_sum_get_well_var( resp, 1, "W_2", "WOPR" ), 1e-5 );
@@ -2317,6 +2326,12 @@ BOOST_AUTO_TEST_CASE(efficiency_factor) {
         BOOST_CHECK_CLOSE(  23.4,     ecl_sum_get_well_connection_var( resp, 1, "W_2", "CVPR", 2, 1, 1 ), 1e-5 );
         BOOST_CHECK_CLOSE( 234.5,     ecl_sum_get_well_connection_var( resp, 2, "W_2", "CVPR", 2, 1, 2 ), 1e-5 );
 
+        BOOST_CHECK_CLOSE( 0.2, ecl_sum_get_well_var( resp, 1, "W_2", "WEFF" ), 1.0e-5 );
+        BOOST_CHECK_CLOSE( 0.2, ecl_sum_get_well_var( resp, 2, "W_2", "WEFF" ), 1.0e-5 );
+
+        BOOST_CHECK_CLOSE( 0.2 * 0.01, ecl_sum_get_well_var( resp, 1, "W_2", "WEFFG" ), 1.0e-5 );
+        BOOST_CHECK_CLOSE( 0.2 * 0.01, ecl_sum_get_well_var( resp, 2, "W_2", "WEFFG" ), 1.0e-5 );
+
         BOOST_CHECK_CLOSE(      23.4 * 0.2 * 0.01, ecl_sum_get_well_connection_var( resp, 1, "W_2", "CVPT", 2, 1, 1 ), 1e-5 );
         BOOST_CHECK_CLOSE( 2 * 234.5 * 0.2 * 0.01, ecl_sum_get_well_connection_var( resp, 2, "W_2", "CVPT", 2, 1, 2 ), 1e-5 );
 
@@ -2326,23 +2341,30 @@ BOOST_AUTO_TEST_CASE(efficiency_factor) {
         BOOST_CHECK_CLOSE(   0.0       , ecl_sum_get_group_var( resp, 1, "G_2", "GWPI" ), 1e-5 );
         BOOST_CHECK_CLOSE(   0.0       , ecl_sum_get_group_var( resp, 1, "G_2", "GGPI" ), 1e-5 );
 
+        BOOST_CHECK_CLOSE(   0.0       , ecl_sum_get_group_var( resp, 1, "G_2", "GWPI" ), 1e-5 );
+        BOOST_CHECK_CLOSE(   0.0       , ecl_sum_get_group_var( resp, 1, "G_2", "GGPI" ), 1e-5 );
+        BOOST_CHECK_CLOSE(   0.01      , ecl_sum_get_group_var( resp, 1, "G_2", "GEFF" ), 1.0e-5 );
+
         BOOST_CHECK_CLOSE( -10.13 - (20.13 * 0.2 * 0.01), ecl_sum_get_group_var( resp, 1, "G", "GWPP" ), 1e-5 );
         BOOST_CHECK_CLOSE( -10.14 - (20.14 * 0.2 * 0.01), ecl_sum_get_group_var( resp, 1, "G", "GOPP" ), 1e-5 );
         BOOST_CHECK_CLOSE( -10.15 - (20.15 * 0.2 * 0.01), ecl_sum_get_group_var( resp, 1, "G", "GGPP" ), 1e-5 );
         BOOST_CHECK_CLOSE(   0.0                        , ecl_sum_get_group_var( resp, 1, "G", "GWPI" ), 1e-5 );
         BOOST_CHECK_CLOSE(   0.0                        , ecl_sum_get_group_var( resp, 1, "G", "GGPI" ), 1e-5 );
+        BOOST_CHECK_CLOSE(   1.0                        , ecl_sum_get_group_var( resp, 1, "G", "GEFF" ), 1.0e-5 );
 
         BOOST_CHECK_CLOSE( -20.13 * 0.2, ecl_sum_get_group_var( resp, 2, "G_2", "GWPP" ), 1e-5 );
         BOOST_CHECK_CLOSE( -20.14 * 0.2, ecl_sum_get_group_var( resp, 2, "G_2", "GOPP" ), 1e-5 );
         BOOST_CHECK_CLOSE( -20.15 * 0.2, ecl_sum_get_group_var( resp, 2, "G_2", "GGPP" ), 1e-5 );
         BOOST_CHECK_CLOSE(   0.0       , ecl_sum_get_group_var( resp, 2, "G_2", "GWPI" ), 1e-5 );
         BOOST_CHECK_CLOSE(   0.0       , ecl_sum_get_group_var( resp, 2, "G_2", "GGPI" ), 1e-5 );
+        BOOST_CHECK_CLOSE(   0.01      , ecl_sum_get_group_var( resp, 2, "G_2", "GEFF" ), 1.0e-5 );
 
         BOOST_CHECK_CLOSE( -10.13 - (20.13 * 0.2 * 0.01), ecl_sum_get_group_var( resp, 2, "G", "GWPP" ), 1e-5 );
         BOOST_CHECK_CLOSE( -10.14 - (20.14 * 0.2 * 0.01), ecl_sum_get_group_var( resp, 2, "G", "GOPP" ), 1e-5 );
         BOOST_CHECK_CLOSE( -10.15 - (20.15 * 0.2 * 0.01), ecl_sum_get_group_var( resp, 2, "G", "GGPP" ), 1e-5 );
         BOOST_CHECK_CLOSE(   0.0                        , ecl_sum_get_group_var( resp, 2, "G", "GWPI" ), 1e-5 );
         BOOST_CHECK_CLOSE(   0.0                        , ecl_sum_get_group_var( resp, 2, "G", "GGPI" ), 1e-5 );
+        BOOST_CHECK_CLOSE(   1.0                        , ecl_sum_get_group_var( resp, 2, "G", "GEFF" ), 1.0e-5 );
 
         /* WEFAC 0.3 assigned to W_3.
          * W_3 assigned to group G3. GEFAC G_3 = 0.02
@@ -2351,6 +2373,12 @@ BOOST_AUTO_TEST_CASE(efficiency_factor) {
 
         BOOST_CHECK_CLOSE( 300.2 / 300.1, ecl_sum_get_well_connection_var( resp, 2, "W_3", "CGOR", 3, 1, 1 ), 1e-5 );
 
+        BOOST_CHECK_CLOSE( 0.3, ecl_sum_get_well_var( resp, 1, "W_3", "WEFF" ), 1.0e-5 );
+        BOOST_CHECK_CLOSE( 0.3, ecl_sum_get_well_var( resp, 2, "W_3", "WEFF" ), 1.0e-5 );
+
+        BOOST_CHECK_CLOSE( 0.3 * 0.02 * 0.03, ecl_sum_get_well_var( resp, 1, "W_3", "WEFFG" ), 1.0e-5 );
+        BOOST_CHECK_CLOSE( 0.3 * 0.02 * 0.04, ecl_sum_get_well_var( resp, 2, "W_3", "WEFFG" ), 1.0e-5 );
+
         BOOST_CHECK_CLOSE( 432.1 * 0.3 * 0.02 * 0.03,
                            ecl_sum_get_well_connection_var( resp, 1, "W_3", "CVPT", 3, 1, 1 ), 1e-5 );
         BOOST_CHECK_CLOSE( 432.1 * 0.3 * 0.02 * 0.03 +
@@ -2366,24 +2394,28 @@ BOOST_AUTO_TEST_CASE(efficiency_factor) {
         BOOST_CHECK_CLOSE( 30.15 * 0.3, ecl_sum_get_group_var( resp, 1, "G_3", "GGPP" ), 1e-5 );
         BOOST_CHECK_CLOSE(  0.0       , ecl_sum_get_group_var( resp, 1, "G_3", "GWPI" ), 1e-5 );
         BOOST_CHECK_CLOSE(  0.0       , ecl_sum_get_group_var( resp, 1, "G_3", "GGPI" ), 1e-5 );
+        BOOST_CHECK_CLOSE(  0.02      , ecl_sum_get_group_var( resp, 1, "G_3", "GEFF" ), 1.0e-5 );
 
         BOOST_CHECK_CLOSE( 30.13 * 0.3 * 0.02, ecl_sum_get_group_var( resp, 1, "G_4", "GWPP" ), 1e-5 );
         BOOST_CHECK_CLOSE( 30.14 * 0.3 * 0.02, ecl_sum_get_group_var( resp, 1, "G_4", "GOPP" ), 1e-5 );
         BOOST_CHECK_CLOSE( 30.15 * 0.3 * 0.02, ecl_sum_get_group_var( resp, 1, "G_4", "GGPP" ), 1e-5 );
         BOOST_CHECK_CLOSE(  0.0              , ecl_sum_get_group_var( resp, 1, "G_4", "GWPI" ), 1e-5 );
         BOOST_CHECK_CLOSE(  0.0              , ecl_sum_get_group_var( resp, 1, "G_4", "GGPI" ), 1e-5 );
+        BOOST_CHECK_CLOSE(  0.03             , ecl_sum_get_group_var( resp, 1, "G_4", "GEFF" ), 1.0e-5 );
 
         BOOST_CHECK_CLOSE( 30.13 * 0.3, ecl_sum_get_group_var( resp, 2, "G_3", "GWPP" ), 1e-5 );
         BOOST_CHECK_CLOSE( 30.14 * 0.3, ecl_sum_get_group_var( resp, 2, "G_3", "GOPP" ), 1e-5 );
         BOOST_CHECK_CLOSE( 30.15 * 0.3, ecl_sum_get_group_var( resp, 2, "G_3", "GGPP" ), 1e-5 );
         BOOST_CHECK_CLOSE(  0.0       , ecl_sum_get_group_var( resp, 2, "G_3", "GWPI" ), 1e-5 );
         BOOST_CHECK_CLOSE(  0.0       , ecl_sum_get_group_var( resp, 2, "G_3", "GGPI" ), 1e-5 );
+        BOOST_CHECK_CLOSE(  0.02      , ecl_sum_get_group_var( resp, 2, "G_3", "GEFF" ), 1.0e-5 );
 
         BOOST_CHECK_CLOSE( 30.13 * 0.3 * 0.02, ecl_sum_get_group_var( resp, 2, "G_4", "GWPP" ), 1e-5 );
         BOOST_CHECK_CLOSE( 30.14 * 0.3 * 0.02, ecl_sum_get_group_var( resp, 2, "G_4", "GOPP" ), 1e-5 );
         BOOST_CHECK_CLOSE( 30.15 * 0.3 * 0.02, ecl_sum_get_group_var( resp, 2, "G_4", "GGPP" ), 1e-5 );
         BOOST_CHECK_CLOSE(  0.0              , ecl_sum_get_group_var( resp, 2, "G_4", "GWPI" ), 1e-5 );
         BOOST_CHECK_CLOSE(  0.0              , ecl_sum_get_group_var( resp, 2, "G_4", "GGPI" ), 1e-5 );
+        BOOST_CHECK_CLOSE(  0.04             , ecl_sum_get_group_var( resp, 2, "G_4", "GEFF" ), 1.0e-5 );
 
         BOOST_CHECK_CLOSE( - 10.13
                            - (20.13 * 0.2 * 0.01)