The proposed Nabucco pipeline between Turkey and Austria is an important part of the EU's Southern Gas Corridor project to bring Caspian Sea and Middle Eastern gas to Europe, reducing its dependence on Russian energy.
"From a political perspective, it's clear that the European Commission supports Nabucco and from discussions with the President of Azerbaijan, I understood that Azerbaijan also supports the project," Barroso said at a press conference in Baku.
Doubts had been raised about the future of the multi-billion-dollar Nabucco project because it has not so far secured enough supplies of gas to make it viable, so backing from energy-rich Azerbaijan represents a significant boost.
On Thursday, Barroso signed what he described as a "breakthrough" agreement with Azerbaijani President Ilham Aliyev which commits the ex-Soviet state to providing substantial long-term gas supplies to EU countries.
Barroso said it was an important step towards creating the Southern Gas Corridor, which envisages the construction of several pipelines including Nabucco.
The EU sees the Southern Gas Corridor project as vital to future energy security after disputes that disrupted supplies of Russian gas to some European countries.
The declaration stated that Azerbaijan will be a "substantial contributor" to the Southern Gas Corridor but did not specify the volume of gas that would be provided, when supplies might begin, or whether they would be destined for the Nabucco pipeline.
Azerbaijan's large energy resources are coveted by its neighbours Russia and Iran as well as by the West.
Baku agreed in September to increase gas exports to Russia to two billion cubic metres this year and increase them further from 2012. On Wednesday, Baku also agreed a five-year deal with Tehran to supply the Islamic republic with a minimum of one billion cubic metres of gas each year.
Later on Friday, Barroso is expected to travel to Turkmenistan, which also has large gas reserves and is another potential source for the proposed new fuel transit route to Europe.