Four activists have been arrested in London and five in Edinburgh.
Sources at Shell said the protests had caused minor disruption at a "very small number" of sites.
The group's members have been using the emergency shut-off switch at petrol stations to stop fuel supplies to the pumps, then removing a fuse to prevent staff from turning it back on immediately.
Protesters climbed on to the roof of several stations, mounting a giant polar bear puppet over one forecourt in Battersea, southwest London.
The action is part of Greenpeace's "Save The Arctic" campaign, which aims to stop oil exploration and industrial fishing in the region by having it recognised as a world park.
Greenpeace campaigners claim competition for oil in the region could spark an "Arctic oil rush".
The organisation has won support for it's campaign against drilling and fishing in the Arctic from celebrities including Sir Paul McCartney, Penelope Cruz, Robert Redford, One Direction, Alexandra Burke, Jarvis Cocker and Sir Richard Branson.
Greenpeace campaigner Sara Ayech, who was at the station in Battersea, said: "An oil spill in the Arctic would be catastrophic for wildlife such as walruses and whales, and Shell knows full well that it would be impossible to clean up after such devastation."
Sources at Shell said a "very small number" of its 580 UK forecourts had been affected by the action and most services had returned to normal soon after the protests.
A Shell spokeswoman said: "Shell recognises that certain organisations are opposed to our exploration programme Offshore Alaska, and we respect the right of individuals and organisations to engage in a free and frank exchange of views about our operations.
"Recognising the right of individuals to express their point of view, we only ask that they do so with their safety and the safety of others, including the general public and Shell personnel, in mind."
The company said it had met with organisations and individuals opposed to drilling off Alaska and had also offered to hold talks with Greenpeace.