PetroVietnam and ExxonMobil have signed an agreement on the development and gas sales for the Ca Voi Xanh (CVX) field offshore Vietnam, the country's biggest gas discovery. CVX is aiming to supply around five tcf from 2023, to five power plants with a combined capacity of 3,750 MW. We estimate a total project cost of around US$20 billion, which would make it Vietnam's biggest upstream/power project. Agreeing a gas price clears a crucial commercial hurdle, and the project can now proceed to pre-FEED. However, CVX must still compete commercially with ExxonMobil's other pre-FID projects to stand a chance of achieving sanction by 2020.