A fuel system for an engine, comprising: a fuel circuit (101,201); a primary fuel pump (103,203) in fluid communication with the fuel circuit configured to pump insufficient fuel flow to the engine for running the engine at at least one engine speed or speed range, wherein the primary fuel pump is mechanically driven and mechanically connected to the engine such that the primary fuel pump is configured to pump fuel as a function of engine speed; a supplemental fuel pump (105,205) in fluid communication with the fuel circuit that is configured to selectively pump fuel to the engine at least during the at least one engine speed or speed range to supplement fuel flow from the primary fuel pump to provide sufficient total fuel flow to the engine for running the engine at all engine speeds; and characterized in that: the supplemental fuel pump is not mechanically connected to the engine and is operatively connected to a turbine disposed in fluid communication with the fuel circuit downstream of the primary fuel pump such that the turbine is configured to be driven by fuel flow from the primary fuel pump; and wherein the fuel circuit further comprises at least two parallel branches downstream of the primary fuel pump, wherein the turbine is in fluid communication with a first branch of the at least two parallel branches; and further comprising a control valve disposed in fluid communication with a second branch of the at least two parallel branches, wherein the control valve is configured to selectively allow and/or meter fuel flow therethrough to create a bypass path around the turbine to selectively allow and/or meter flow through the turbine, and thus a speed of the supplemental fuel pump, and wherein the control valve is configured to shut off flow in the second branch to control fuel flow to the turbine, wherein the primary fuel pump is connected via the first branch to the turbine without a valve therebetween to provide uninterrupted flow to the turbine, and wherein the first branch and the second branch both lead to a combustor. a fuel circuit (101,201); a primary fuel pump (103,203) in fluid communication with the fuel circuit configured to pump insufficient fuel flow to the engine for running the engine at at least one engine speed or speed range, wherein the primary fuel pump is mechanically driven and mechanically connected to the engine such that the primary fuel pump is configured to pump fuel as a function of engine speed; a supplemental fuel pump (105,205) in fluid communication with the fuel circuit that is configured to selectively pump fuel to the engine at least during the at least one engine speed or speed range to supplement fuel flow from the primary fuel pump to provide sufficient total fuel flow to the engine for running the engine at all engine speeds; and characterized in that: the supplemental fuel pump is not mechanically connected to the engine and is operatively connected to a turbine disposed in fluid communication with the fuel circuit downstream of the primary fuel pump such that the turbine is configured to be driven by fuel flow from the primary fuel pump; and wherein the fuel circuit further comprises at least two parallel branches downstream of the primary fuel pump, wherein the turbine is in fluid communication with a first branch of the at least two parallel branches; and