Tony Hayward, BP's chief executive, has attempted to dampen growing investor anger over its oil sands activities by publicly pledging for the first time not to use mining techniques that devastate the landscape.

But the pledge was not enough to head off a significant rebellion from a growing group of increasingly environmentally aware investors at its annual general meeting today.

Environmentalists also poured scorn on the promise, which was also made in BP's sustainability report published today. BP said it would only ever use 'in-situ' drilling techniques in Canada, rather than open-pit mining, which also results in more water pollution.

John Sauven, executive director of Greenpeace, said the pledge was like "quitting Benson and Hedges in favour of Rothmans". A report out last month from environmental group the Pembina Institute said that while in-situ techniques result in lower nitrogen oxide emissions, and are less damaging to the landscape and rivers, they typically cause more greenhouse gas and sulphur dioxide emissions than mining because of the highly energy intensive process required to extract the oil from underground and process it.

BP's oil sands projects in Canada, which have not yet begun production, only involve in-situ drilling. A spokesman said that the company's experience in reservoir management and drilling techniques were more relevant to this technique, which was the main factor behind the pledge. He said that environmental considerations also played a part.

But Sauven said: "BP is trying to fool the public by ruling out giant and visually shocking mines when what it's doing below the ground is even more damaging to the climate."

Today, a group of 143 shareholders tabled a resolution demanding the oil firm review the risks of its Sunrise oil sands development in Alberta. BP will decide by the end of the year whether to go ahead with the $2.4bn (£1.5bn) joint venture with Husky Energy. BP successfully fought off the resolution, but nearly 15% of shareholders showed their support for the protest by either voting in favour or abstaining.

The protest was backed by several large investors including Calpers and Calstrs, the California state employees' and teachers' pensions funds, and Co-operative Asset Management in the UK.

Canada holds estimated reserves of 179bn barrels of oil, the majority found in oil sands, notionally putting it second only to Saudi Arabia. But oil sands production has been estimated to cause three times as much greenhouse gas emissions as conventional extraction.

Representatives from affected Canadian communities also pleaded for the Sunrise project to be stopped, saying that oil sands had resulted in a "terrifyingly high rate of cancer" in the area. George Poitras, a former chief of the Mikisew Cree First Nation said: "That's why we no longer call it 'dirty oil' but 'bloody oil'. The blood of Fort Chipewyan people is on these companies' hands."

Outside the meeting, a small group of protesters said they wanted to raise awareness about the damage caused by extracting oil sands. One man told the Guardian he was planning to light a bottle of petrol and throw it at the conference centre to "get the public to open their eyes to the inevitability of catastrophic climate change if we keep up this carbon-intensive capitalist system." He later said he had been persuaded to remain peaceful.

The organisers of the resolution, responsible investment charity FairPensions, said the shareholder revolt marked turning point in how people engaged with the investment of their pension savings. More than 5,000 individuals joined an internet campaign petitioning their pension providers to back the resolution.