How Much CO2 Do Oil Tankers Emit?

Why It Matters

Tanker‑related emissions add a hidden layer to California’s climate challenge, and policy shifts toward domestic production could lower greenhouse‑gas output while enhancing energy security.

Key Takeaways

• California imported 373 million barrels in 2025.
• Domestic production fell 72% from 1986 to 2025.
• Tanker emissions add significant CO₂ to supply chain.
• War in Middle East increases shipping distances and fuel use.
• Reducing imports could cut emissions and boost energy security.

Pulse Analysis

Maritime transport accounts for roughly 3% of global CO₂ emissions, and oil tankers are among the most carbon‑intensive vessels due to their reliance on heavy bunker fuel. When crude is shipped from the Middle East to West Coast refineries, each voyage can emit up to 150,000 metric tons of CO₂, equivalent to the annual output of several thousand passenger cars. For California, which consumed 484 million barrels in 2025, the cumulative impact of these voyages adds a substantial, often overlooked, component to the state’s overall greenhouse‑gas inventory.

The ongoing conflict in the Middle East has disrupted traditional supply chains, prompting shippers to take longer, less efficient routes around the Cape of Good Hope or through the Suez Canal under congested conditions. These detours increase fuel consumption and extend voyage times, amplifying emissions per barrel delivered. Moreover, the predominance of high‑sulfur bunker fuel—still widely used despite IMO regulations—means that each tanker contributes not only CO₂ but also nitrogen oxides and particulate matter, worsening air quality along coastal ports.

For California policymakers, the data underscores a strategic lever: curbing imported crude can directly reduce maritime emissions while revitalizing in‑state production that peaked at 402 million barrels in 1986. Investing in cleaner refinery technologies, incentivizing low‑carbon shipping contracts, and expanding renewable diesel blends can together shrink the carbon intensity of the entire fuel supply chain. As climate goals tighten, aligning energy security with emissions reductions will become a decisive factor for the state’s future energy mix.