The suspects, identified as Noel Portillo, 22, and Ricardo Robles, 24, were arrested early Friday at the McDonald's, the Riverside (Calif.) Press-Enterprise reported.
Police were tipped off to the alleged heist by the restaurant owner, who said thieves have been targeting restaurants and stealing thousands of dollars worth of cooking grease to resell to recyclers. Recyclers then turn the grease into biodiesel fuel.
The McDonald's owner, whose name was not reported, told police around midnight that he would be waiting inside his restaurant and would call again if the suspects arrived. Around 1:50 a.m. he called police to say the suspects were at the restaurant stealing grease.
When authorities arrived they found Portillo and Robles sitting inside a Dodge Ram with a large metal tank mounted on the bed, the Los Angeles Times reported.
Police reviewed surveillance footage before arresting the pair.