Abstract: CO₂ huff-and-puff is an effective method in the development of extra-low permeability and ultra-low permeability reservoirs.In order to use this technique to cut the cost and increase oil recovery in oilfields,the gas utilization ratio during CO₂ huff-and-puff process was investigated.CO₂ huff-and-puff tests using ultra-low permeability cores from Changqing Oilfield were carried out to investigate oil recovery factors and CO₂ utilization under different injection pressures.The test results show that ultimate oil recovery increases with the increase of injection pressure and the increasing amplitude would decrease gradually.In addition,CO₂ utilization ratio is relatively high in the first four cycles,but is significantly reduced with the increase of huff-and-puff cycles.The increasing of injection pressure can make the CO₂-crude oil system enter into a miscible phase condition, which is beneficial for obtaining higher oil recovery without significant increase of the cost of CO₂ supply.The results show that CO₂ huff-and-puff with four cycles will be close to miscible condition and could achieve better development effect and economic benefits.