A study was conducted to determine the feasibility of fieldscale CO2 enrichment of vegetable crops grown under tunnel culture. Cucumber, squash and tomato were grown under polyethylene tunnels in a manner similar to commercial practices in southern California. The buried drip irrigation system was used to uniformly deliver an enriched CO2 air stream independent of irrigation. CO2 concentration in the tunnel atmosphere was maintained between 700-1000 ppm during daylight hours. Enrichment began two weeks after planting and continued for four weeks. At the end of the treatment phase, enrichment had significantly increased plant dry weights. This growth advantage continued through harvest, with enriched plots yielding 20%, 30% and 32% more fruit of squash, cucumber and tomato, respectively. As performed in this study, the expense of CO2 enrichment represented less than a 10% increase in total pre-harvest costs. Industrial bottled CO2 was used in this study; since bottled CO2 is captured as a byproduct of industrial processes, this usage represents a recycling of CO2 that would otherwise be vented directly to the atmosphere.