Brent crude futures rose above $108 per barrel on Monday as tensions between Russia and the West escalated over the latest twist in the Ukraine crisis.
Separatist rebels in eastern Ukraine hailed a landslide victory in Sunday's referendum, which has been dismissed by Ukraine's leaders and the West as illegal.
Moscow welcomed the results of the referendum and called for the results to be implemented in a "civilised" manner.
Brent for June delivery gained 27 cents at $108.16 by 0645 GMT while US June crude gained 11 cents to $100.10 per barrel.
Concerns that the geopolitical tensions between Russia and the West could prompt Russia to restrict energy supplies to Europe have influenced the price of oil as the crisis has evolved.
European leaders could vote to strengthen sanctions against Russia when foreign ministers from across the bloc meet on Monday. The EU will decide whether to extend the sanctions it imposed on Moscow after Russia backed a similar referendum in Crimea in March.
Currently sanctions imposed by Brussels and Washington have been limited to asset freezes and travel bans on a number of individuals and their companies with close ties to the Kremlin. However, Washington has mooted a broader range of sanctions that could target entire sectors of the Russian economy, including finance, mining and energy.
The European Union relies on Russia for around a third of its gas needs, 40% of which comes through Ukraine.