Oil prices plunged to new lows Tuesday on renewed concerns about a global supply glut, extending a selloff that has rattled financial markets, driven down shares of energy companies and stoked alarm among government officials. U.S. oil futures fell $1.59, or 2%, to $77.19 a barrel, a fresh three-year low, and Brent crude, the global benchmark, slid $1.96, or 2.3%, to $82.82 a barrel, a new four-year low. Saudi Arabia’s surprise price cut for its U.S. oil deliveries this week has driven the latest swoon, with U.S. oil prices down 4% since the announcement. The move suggests the world’s largest oil exporter is more concerned with maintaining production volume and market share than shoring up prices through output cuts, experts say.