Teekay Tankers (TNK) shares ended the last trading session 7.4% higher at $55.96. The jump came on an impressive volume with a higher-than-average number of shares changing hands in the session. This compares to the stock's 17.5% gain over the past four weeks.This was the third consecutive day of share price increase for the shipping company. In fact, TNK shares have performed well over the past month, gaining 21%. Gradual improvement in the tanker market contributed to the uptick.This oil and gas shipping ...