Total development activity for the two-state area was down slightly from last year. Exploratory tests totaled 838, a decrease of 156 from last year, while development drilling increased to 735 wells or 49 more than 1957. Eight counties in the Denver basin accounted for 66.5% of all the exploratory tests drilled in the two states.

Colorado showed an increase in total drilling of 6.5% over 1957 much of which was due to field development and exploration on the "Western Slope."

Nebraska activity decreased nearly 18% due to a sharp reduction in exploratory drilling both in the Denver basin and on the west flank of the Cambridge arch.

Success ratios for exploratory tests increased about 1½% for both states, but again Colorado's "Western Slope" with its ratio of more than 19% was responsible for this gain.

There were 34 oil pools and 30 gas pools discovered in Colorado. Most of the gas pools were in the Piceance basin.

Nebraska had 45 pools discovered, all of which were oil producers. None of the 1958 discoveries in either state is likely to achieve major field status.

The exploratory activity trend in the Denver basin has become well established as northward and eastward into Nebraska.

Deeper drilling on the "Western Slope" of Colorado was evident with many tests in the southwestern corner going into the Paradox member of the Hermosa formation.

Extreme eastern Colorado's Las Animas arch had very heavy leasing activity following early year successes in the Pennsylvanian of northwestern Kansas. An active lease play also followed the announcement of a 12-well exploratory program in the northern part of the Raton basin.