Sounds like worst case is $11B over 10 years or about 5% to 6% of current annual cash flow. And, the upside appears to be the rumored settlement that they could reduce the burden 80%, if they pay $2.2B up-front. Seems to me that given results, worst case is already more than priced in and upside to best case could be substantial.
worst is priced in...stocks trading at ~5.0x EV/2014 EBITDA vs. RIO and BHP trading about 7.3-7.5x...the discount is because the street expects them to get hit with the tax bill...final settlement will result in a major overhang lift on the shares, so positive.
also, the government offered them a 15 year deal to pay off the taxes...they won't have to swallow the nut all at one time. buy the pain