After enjoying July, August and September trading above Cushing DSW, Midland West Texas Sour (WTS) dropped from a $1.40/bbl premium in mid-August to a discount of $(0.71)/bbl on Friday. While WTS is a thin market subject to substantial daily volatility the recent decline has been steeper than usual (right graph). According to RBN’s TradeView report, a lack of refinery buying for WTS was reported last week. Also, P66’s Borger refinery, which processes primarily medium sour crude oil, had 30 Mb/d offline for maintenance, which could have reduced the company’s WTS purchases.
Note that over the long term (left graph), WTS averages about $0.20/bbl below Cushing DSW, but can average above zero when sour crude is in short supply, such as in 2021.