U.S. oil and gas companies are scrambling for credit, with lenders tightening their purse strings as oil prices continue to sit below $40 per barrel. Oil and gas lenders have restricted the borrowing abilities for oil and gas companies to the tune of 20% so far this spring lending season, according to a Reuters analysis. It’s supposed to be a negotiation between the companies and the lenders. Available credit is, twice each year, reassessed, based on the value of a companies’ reserves. Well, those valuations are off substantially…