A high-pressure fuel pump for gasoline direct injection and comprising: a pump housing which defines a pumping chamber , a fuel inlet which allows low-pressure fuel into said pumping chamber , a fuel outlet which allows high-pressure fuel out of said pumping chamber , and a plunger bore which extends along an axis and opens into said pumping chamber ; and a pumping plunger which reciprocates within said plunger bore along said axis such that reciprocation of said pumping plunger within said plunger bore increases and decreases a volume of said pumping chamber , such that low-pressure fuel flows from said fuel inlet to said pumping chamber when said volume increases, and high-pressure fuel is discharged from said pumping chamber through said fuel outlet when said volume decreases; wherein the pumping plunger is attached to a cam follower which is contactable with a camshaft , configured to drive reciprocating movement of the pumping plunger , and wherein a return spring is compressed axially between the pump housing and the cam follower to maintain the cam follower in contact with the camshaft , in use, wherein said pumping plunger includes a sealing ring groove which is concentric with said plunger bore , said sealing ring groove including a sealing ring therein, for preventing fuel from escaping the pumping chamber between the interface of the pumping plunger and plunger bore , wherein the sealing ring engages said plunger bore in an interference fit, such that said sealing ring is held in radial compression by said pumping plunger and said plunger bore ; and wherein said sealing ring is held in axial compression within said sealing ring groove ; and wherein a diametric clearance in the range of 13 to 30 microns is provided between said pumping plunger and said plunger bore . a pump housing which defines a pumping chamber , a fuel inlet which allows low-pressure fuel into said pumping chamber , a fuel outlet which allows high-pressure fuel out of said pumping chamber , and a plunger bore which extends along an axis and opens into said pumping chamber ; and a pumping plunger which reciprocates within said plunger bore along said axis such that reciprocation of said pumping plunger within said plunger bore increases and decreases a volume of said pumping chamber , such that low-pressure fuel flows from said fuel inlet to said pumping chamber when said volume increases, and high-pressure fuel is discharged from said pumping chamber through said fuel outlet when said volume decreases; wherein the pumping plunger is attached to a cam follower which is contactable with a camshaft , configured to drive reciprocating movement of the pumping plunger , and wherein a return spring is compressed axially between the pump housing and the cam follower to maintain the cam follower in contact with the camshaft , in use, wherein said pumping plunger includes a sealing ring groove which is concentric with said plunger bore , said sealing ring groove including a sealing ring therein, for preventing fuel from escaping the pumping chamber between the interface of the pumping plunger and plunger bore , wherein the sealing ring engages said plunger bore in an interference fit, such that said sealing ring is held in radial compression by said pumping plunger and said plunger bore ; and wherein said sealing ring is held in axial compression within said sealing ring groove ; and wherein a diametric clearance in the range of 13 to 30 microns is provided between said pumping plunger and said plunger bore . <EOS>