If we started drilling in the U.S. how long will it last before we are back at square one?

Most of the USA has been adequately explored for oil, with the exception of areas protected such as National Parks etc.

Drilling more wells will increase production but reduce the life span of reserves.

Time to sell that SUV!

Surprise! We started drilling in the U.S. 160 years ago, assuming you are talking about oil drilling. For the first hundred years we were the world's biggest producer. We reached peak production around 1970, and have been producing less every year since then. Maybe you would like to rephrase the question.

We would be back to square one before we started. It would take years and lots of money before we started seeing any results. By the time we did, we would have wasted that money. The oil would be sucked up so fast and then we would start over. Right now, the US uses 25% of the oil in the world and the untapped reserves in the US are predicted to cover 3% of that.

A drill hole is round so you could never get back to square one.