CO2 emitted during the extraction of oil and gas accounts for less than 4% of total emissions associated with fossil fuels; nearly 90% of emissions occur in their final combustion. And very few countries currently require producers to either pay a carbon tax or participate in an emissions trading scheme. But prudent upstream companies are assuming that carbon charges are a question of when, not if, and including these variables in their asset valuation models. This analysis addresses the following questions: Where do upstream carbon charges currently exist, and how do they interact with other fiscal terms? What are the differences between carbon charges introduced in royalty/tax and production sharing contract (PSC) fiscal systems? What is the potential impact of carbon charges on upstream asset values?