An oil burner engine is a steam engine that uses oil as its fuel. The term is usually applied to a locomotive or ship engine that burns oil to heat water, to produce the steam which drives the pistons, or turbines, from which the power is derived.

This is mechanically very different from diesel engines, which use internal combustion, although they are sometimes colloquially referred to as oil burners.

Oil-burning steam engines first appeared in the latter half of the 19th century, but their use remained largely confined to regions such as the Caspian and southern Russia, where oil was abundant and coal scarce. Oil burning steam engines were used more extensively in ships and trains during the first half of the 20th century, before the widespread adoption of diesel engines rendered the technology largely obsolete.

In the 21st century, oil‑fired steam locomotives have become popular with heritage railway operators due to inherent advantages relative to coal, including reduced wildfire risk, lower maintenance requirements, and improved emissions performance.

A variety of experimental oil powered steam boilers were patented in the 1860s. Most of the early patents used steam to spray atomized oil into the steam boilers furnace. Attempts to burn oil from a free surface were unsuccessful due to the inherently low rates of combustion from the available surface area.

On 21 April 1868, the steam yacht Henrietta made a voyage down the river Clyde powered by an oil fired boiler designed and patented by a Mr Donald of George Miller & Co. Donald's design used a jet of dry steam to spray oil into a furnace lined with fireproof bricks. Prior to the Henrietta’s oil burner conversion, George Miller & Co was recorded as having used oil to power their works in Glasgow for a “considerable time”.

During the late 19th century numerous burner designs were patented using combinations of steam, compressed air and injection pumps to spray oil into boiler furnaces. Most of the early oil burner designs were commercial failures due to the high cost of oil (relative to coal) rather than any technical issues with the burners themselves.

During the early 20th century, marine and large oil burning steam engines generally used electric motor or steam driven injection pumps. Oil would be drawn from a storage tank through suction strainers and across viscosity-reducing oil heaters. The oil would then be pumped through discharge strainers before entering the burners as a whirling mist. Combustion air was introduced through special furnace-fronts, which were fitted with dampers to regulate the supply. Smaller land-based oil burning steam engines typically used steam jets fed from the main boiler to blast atomized oil into the burner nozzles.