The article looks at how mergers affect market share, focusing on the impact of merger-specific efficiencies. By studying the divestiture of Texaco's Canadian assets, the researchers found that merged firms tend to regain market share in the long run. They used a difference-in-difference approach to compare changes in market shares for the merging firm with other similar firms. Despite some biases in their estimates, the overall trend of market share effects was consistently identified. This method provides a valuable way to analyze merger effects compared to traditional across-market comparisons.