I received estimates from several firms. Alpha Environmental Services was neither the most expensive nor the least. They were, however, half the cost of our most expensive estimate. We went with them because of their reputation (thanks, Angie's List), promptness, and professionalism, and because they have the appropriate DEQ licenses so we could be sure that the tank would be properly decommissioned. They basically took care of everything from initial soil test (I forget their technician's name, but he very kindly explained the process for me when he came to take soil samples) to the cleaning the oil tank, filling with inert material, and removal of vent and inlet. We had excellent communication throughout the process and received documents with lab results and certifying the decommissioning within a day or two. If we have need of other environmental services, we will certainly call on them again.