Goldman Sachs analyst John Nelson downgraded Alta Mesa Resources to Neutral and lowered his price target for the shares to $2.50 from $6.50. Management commentary on the Q3 conference call has "widened the confidence interval" around Alta Mesa's medium-term volume growth trajectory/inventory depth, which will likely push out investor appreciation of its STACK resource base, Nelson tells investors in a research note. The analyst also raised his long-term Meramec/Osage well cost expectation and reduced his 2018-2020 estimated annual volume growth by 12 percentage points.