PITTSBURGH (KDKA) — Big multi-national oil companies are gobbling up little companies to drill in the Marcellus Shale.

Demonstrators in Pittsburgh are worried about the environmental impact and that companies like Exxon pay their fair share.

The marchers say big oil will get a free ride in Pennsylvania and argue for a state severance tax on drilling.

But with Shell, Chevron and Exxon stepping up their game, they’re also worried about acceleration in drilling.

Given the recent environmental disasters, they say bigger is not better.

“BP just last year we saw what happened in the Gulf Coast,” Ian Sulkowski, of One Pittsburgh, said.

Exxon is still saddled with the legacy of the Valdez oil spill.

“How they could have easily prevented the situation and how after it happened they choose to ignore essentially the needs of the people that were affected,” Andrew Wagner, of Sewickley, said.

But given those disasters, CMU professor Kelvin Gregory says Exxon and the other big oil companies will be less likely to repeat the mistakes of the past.

“The larger producers are going to feel like they’ve got more at stake in terms of their stewardship of the environment,” Gregory said.

Exxon Mobil is purchasing two companies, including Phillips Resources and its 200 employees in Warrendale, but what they’re really purchasing is lease acreage – 317,000 acres of land ready for drilling.

“This is a land rush for the big producers to start holding those new leases,” Gregory said.

The big corporations are staking out territory in counties like Butler, Washington, Greene and Fayette.

They’ve turned their attention to natural gas in general and the Marcellus in particular now that increased worldwide demand for oil is drying up reserves.

“It solidifies the reality of the Marcellus Shale in both producers’ and consumers’ minds,” Gregory said.