Diamond S Shipping Group, a medium range product tanker operator backed by Wilbur Ross, postponed its IPO on Tuesday. The Greenwich, CT-based company was founded in 2007 and booked $178 million in sales for the 12 months ended December 31, 2013. Diamond S Shipping Group initially filed confidentially on September 18, 2013. Jefferies and BofA Merrill Lynch were set to be the joint bookrunners on the deal.