The giant container ship Emma Maersk burns 350 tons of fuel a day and "can emit more than 300,000 tonnes of CO2 a year - equivalent to a medium-sized coal power station." Thats according to a February 13 article in The Guardian article: Shipping boom fuels rising tide of global CO2 emissions.
Calculate your ship's CO2 emissions at SustainableShipping.
gcaptain has green ships covered here.
BunkerWorld sorts out IFO, MDO, MGO here