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.