HOUSTON — Two Texas oil companies joined forces on Wednesday in the biggest deal yet in the Southwestern oil patch, one that should add momentum to the rush to produce more oil as prices rise.

The creation of a shale-oil colossus comes at a precarious moment, when production in the region is expanding so fast that pipeline construction is barely keeping up. That may cap the potential of the deal, at least over the next year or two, to get oil to the market profitably.

The move by Concho Resources to purchase RSP Permian for $9.5 billion will make it the biggest shale oil and natural gas producer in the Permian Basin, the oil-rich area. With 27 rigs, the company said it would have the area’s largest drilling and hydraulic fracturing operation and a reach of 640,000 acres.

Much larger companies, like Exxon Mobil and Chevron, are also increasing their investments in the Permian Basin, where output has doubled to roughly three million barrels a day over the last five years, making it the principal driver of the domestic oil production boom.