SkyWest Inc., a commuter partner of United Airlines and Delta Air Lines Inc., plans to buy or lease 22 regional jets to expand and improve service.

Eighteen of the new planes will fly for United Express, and the other four for Delta Connection, the commuter carrier said in a statement today. SkyWest hasn't selected a manufacturer. Deliveries would start in late 2008.

SkyWest plans to retire 23 Embraer EMB-120 30-seat turboprop aircraft to replace them with 18 jets that have 66 seats each. The St. George, Utah-based airline also will swap out four older 50-seat jets with 76-seat aircraft for.