SPS, thanks for coming back. DOC is Direct Operating Costs: i.e Fuel and maintenance expressed as an hourly rate. Basically all costs that are incurred by actually flying the aircraft. eg the cost of an engine overhaul after 1500 hours can be expressed as an hourly cost.
Not included in here is stuff that you have to pay annually anyway like (usually) insurance, space in a hangar, cost of finance, fat corporate pilot and so on.
I know a DOC can be a bit academic if you buy an aircraft with one hour to go to a major overhaul but it is a useful tool for long term cost projections.
Any info gratefully received. You can e-mail me if you want to keep it private.