Goldman Sachs analyst Eugene King upgraded BHP Billiton (BHP) to Buy with an increased price target of A$35.50.

The analyst expects BHP's cash conversion to reverse in the second half of 2018 following a disappointing first half of the year.

BHP has a number of upcoming catalysts, including the divestment of its onshore assets, to close the 9% valuation gap to Rio Tinto (RIO), King tells investors in a research note.