low oil pressure light came on and engine stalled going 40 mph

What is your question?

car has 280k miles but the engine was changed and then about 70k the head was replaced with a rebuilt head. I have been driving back and forth to Atlantic City a lot in the last couple of months and it has been running fine, I checked my fuel efficiency and its been around 21mpg, I do have an oil leak but I monitor and add oil when necessary, any ideas what may have happened I had it towed to my house this happened last night 8-9-13 and haven't talked to a mechanic yet