The type of pump used varies. Gear pumps trochoid pumps and vane pumps are all commonly used. Plunger pumps have been used in the past, but these are now only used rarely, for small engines.
To avoid the need for priming, the pump is always mounted low-down, either submerged or around the level of the oil in the sump. A short pick-up pipe with a simple wire-mesh strainer reaches to the bottom of the sump.
For simplicity and reliability, mechanical pumps are used, driven by mechanical geartrains from the crankshaft. Reducing pump speed is beneficial and so it is usual to drive the pump from the cam (if this is mounted in the cylinder block) or distributor shaft, which turns at half engine speed. Placing the oil pump low-down uses a near-vertical drive shaft, driven by helical skew gears from the camshaft.
Some engines, such as the Fiat twin cam engine of 1964, began as OHV engines with an oil pump driven from a conventional camshaft in the cylinder block. When the twin overhead cam engine was developed, the previous oil pump arrangement was retained and the camshaft became a shortened stub shaft. Even when the distributor position was moved from the previous block-mount to being mounted on the cylinder head camshafts, the oil pump drive remained in the same position, the unused distributor position now covered by a blanking plate. Small engines, or scooters may have internal gear pumps mounted directly on their crankshaft.
For reliability, it is rare to use an external drive mechanism, either a separate belt drive or external gears, although camshaft-driven pumps often rely on the same timing belt. Additional separate belts are sometimes used where dry sump pumps have been added to engines during tuning.
Electric oil pumps are not used, again for reliability. Some 'turbo timer' electric auxiliary oil pumps are sometimes fitted to turbocharged engines. These are a second oil pump that continues to run after the engine has stopped, providing cooling oil to the hot bearings of a turbocharger for some minutes, whilst it cools down. These are supplementary pumps and do not replace the main, mechanical, oil pump.