Roommate refuses to pay for common utilities?

I share an apartment with 2 roommates. We pay for utilities which include gas and electric. I am on the electric and gas bill and we split it 3 ways. My roommate stopped paying her share of the gas and electric bills (also stopped paying rent but that's our landlord's problem). We live in MA and the gas bills are big especially since the nonpaying roommate is home all day and likes it warm and cozy. What can I do? We had a verbal agreement regarding the utilities, the lease does say we are responsible for them.