The summit, dubbed "Natural Gas for Europe: Security and Partnership", has drawn officials of 28 gas-supplying and gas-recipient countries, as well as representatives of the European Union, including European Commission President Jose Manuel Barroso, the United States and managers of big national gas companies, including Russia's Gazprom, France's Gaz de France, Qatari Gas and Italy's Eni.
Croatia is being represented by President Stjepan Mesic.
Parvanov called for demonstrating more political will and readiness to ensure the provision of energy products.
The Sofia summit is part of efforts made by Bulgaria to advance dialogue among countries in the regions of the Black Sea, the Caspian Sea, Central Asia, the Middle East and the EU.
The event is a sort of continuation of the energy summit held in Zagreb in June 2007.
Although he was expected to attend the summit, Russian Prime Minister Vladimir Putin cancelled his arrival at the last minute.
According to Bulgarian Deputy Prime Minister and Foreign Minister Ivailo Kalfin, Russia has linked Putin's visit to progress in efforts to sign an agreement on the South Stream pipeline project, which will transport natural gas from Russia under the Black Sea via Bulgaria to other European countries.
There is still no agreement on the matter at the level of experts.
The United States and the EU have repeatedly criticised the EUR 10-billion project launched by Gazprom, fearing that its implementation could only increase Europe's dependence on gas supplies from Russia.
The 27-strong European bloc prefers another project called Nabucco, a planned natural gas pipeline that would transport natural gas from Turkey to Austria via Bulgaria, Romania, and Hungary.
Addressing the summit, Mesic said that energy and energy products must not be used as an instrument for achieving political goals or for exerting political pressure.
In a free market, no obstacles should prevent access to energy and distribution networks, Mesic said, calling for creating conditions for healthy competition to strengthen the market and enhance the security of consumers.
Croatia strongly supports efforts to set up a stable, transparent, fair and efficient legal and regulatory system which will ensure the enforcement of adopted agreements, Mesic said.
A joint document of the summit is expected to be adopted on the second day of the summit on Saturday.