No it depends on the contract. Ideally CARRY would be earlier than PRICE but that's not aways possible if you're already trading the front contract. I suggest you read this http://qoppac.blogspot.co.uk/2015/05/systems-building-futures-rolling.html ("The need to measure contango") or appendix B of my book on the carry rule p.285 print edition
GAT
Ok, I re-read the carry section of appendix B, but still I miss something. In Futures: If Trading Nearest Contract, Net return would be a multiple of Price Differential. Price Differential = Next Price - Current price ~= (in the case of WTI currently) 51.3 - 50.8 = 0.5. However, the curve is in contango so I would expect that the Net Return would be a negative number, wouldn`t you say so?