The U.S. oil benchmark for May was back in positive territory Monday night after a wild and historic plunge that saw it close down 306%, at negative-$37.63 a barrel, earlier in the day. West Texas Intermediate crude for May delivery clk20 was last at $1.66 a barrel in overnight electronic trading, up more than 100% in the session. The May crude contract expires on Tuesday; the more actively traded June contract clm20 was last above $21 a barrel, up around 7% from its Monday close at $20.03 a barrel. For more, read: Why oil prices just crashed into negative territory — 4 things investors need to know