The nearest expiration date for Los Angeles CARB Diesel (OPIS) vs. NY Harbor ULSD Futures (Aug 2013) is Aug 30, 2013.
The best time to sell a futures contract is when you've already made money on the investment, but still have plenty of time left before the expiration date. Thus, a good option would be to sell Los Angeles CARB Diesel (OPIS) vs. NY Harbor ULSD Futures (Aug 2013) before Aug 30, 2013.