Activists from That is Rigged are on the Ineos refinery in Grangemouth, Fife, and the Nustar Clydebank oil terminal in West Dunbartonshire.
They claim to have stopped oil leaving the sites and might be seen protesting on the gates, sitting on pipes and on top of a tanker.
The campaign group posted on Twitter: “Grangemouth supplies 90% of Scotland’s oil. We’ve stopped oil leaving this site, in addition to Nustar Terminal in Clydebank. We’ve no plans to stop.
“Groups of persons are currently occupying pipework and a fuel silo and blockading terminal gates, while one other group has immobilised a carpark stuffed with tankers on the Grangemouth facility. No fuel can leave the sites while they’re occupied.
The campaign group added: “The motion is the primary in a sustained series of actions, through which the group has vowed to shut down the Scottish oil industry.”
The group called on the Scottish Government to implement a just transition for oil and gas employees “as a substitute of assisting billionaires like (Ineos owner) Jim Ratcliffe. Dinnae fash yersel (don’t worry), Jim, we’re not going anywhere.”
Police have been called to each sites and Ineos said the Grangemouth terminal has been “temporarily closed to traffic” over safety concerns.
An Ineos spokesperson said: “We’re aware of quite a few protesters on the Petroineos Road Terminal in Grangemouth.
“We’ve mobilised our incident management team and we’re liaising with Police Scotland. The protester motion is confined to a small area of the location and our manufacturing operations remain unaffected.
“We urge the protesters to contemplate the security of themselves, our colleagues and the broader community. Our primary concern is at all times safety. We’re taking steps to make sure the security of all involved and have temporarily closed the terminal to traffic.”
A Police Scotland spokesperson said: “We’re aware of quite a few protesters on the Road Tanker Terminal on the Ineos site in Grangemouth. There’s also a small group gathered on the oil terminal at Rothsay Dock, Clydebank. Officers are in attendance.”
Nustar has been contacted for comment.
Laura Paterson is a reporter for PA Scotland.