Greenpeace contends Arctic drilling poses potentially catastrophic environmental dangers. But Russia bristles at criticism of its oil and gas industry, which is the backbone of the country's economy.
All of those detained were initially charged with piracy, but investigators later changed the charge to hooliganism. Although a lesser charge, hooliganism carries a potential sentence of seven years; piracy's maximum is 15.
One activist was denied bail on Monday, but the approval of bail to others suggested a change in official strategy in the case.
A Greenpeace lawyer said an appeal will be filed to release Australian Colin Russell as well. Russell does not appear to have been singled out in being denied bail; his hearing simply came up first.
"None of our people will be truly free until they are all back home with their families," the group's international executive director Kumi Naidoo said in a statement.
It was not immediately clear whether any of those approved for release would be free to leave the country or move about the city.
On Wednesday, the ship's skipper, Peter Willcox, and four other Greenpeace activists were granted bail of 2 million rubles ($61,500) each.
