ORLEN Lietuva (ex Mažeikių Nafta) is a company centered around the Mažeikiai oil refinery and oil-processing plant in Lithuania. It includes the only refinery in the Baltic States.

The Mažeikiai refinery, located near the town of Mažeikiai, has a design processing capacity of 15 million tons of crude oil per year. However, it is more efficient to process around 8 million tons of crude oil, while using the remaining capacity for processing other feedstock. Historically, the primary feedstock has been Russian crude oil transported via the Druzhba pipeline, however the relevant branch of this system has been closed in Russian territory since July 2006, ostensibly for repairs. Crude oil is now being supplied by the Būtingė Terminal (see below). The Mažeikiai refinery is the only oil refinery in the Baltic States.

Mažeikių Nafta operates a system of pipelines with a total length of around 500 kilometers. This system includes two pump stations near Biržai and another near Joniškis, crude oil pipelines to the Mažeikiai Refinery and Būtingė Terminal, a crude oil pipeline leading to Ventspils, and another products pipeline supplying diesel fuel to the same location. Construction of pipelines in Lithuania started in 1966, with the first crude oil being put through them in 1968. In 1992, the company Naftotiekis was founded for the operation of Lithuanian pipelines, which became part of Mažeikių Nafta in 1998.