The U.S. Energy Department last month reported "unprecedented drops" in Iranian crude oil exports because of U.S. and European sanctions imposed on the energy sector.
Nevertheless, Qasemi said Iran has more oil customers outside the United States and European Union.
"We have other customers today and more than 60 countries today, in fact, are purchasing our petrochemical and oil products and derivatives," he told state-funded broadcaster Press TV. "So we have our presence. We have maintained our presence in the market."
Countries can get waivers from U.S. sanctions if they show "significant" reductions in crude oil purchases from Iran. Sanctions are meant to starve Iran of the funding it may need to support its nuclear program.
Iran kicked off an oil and natural gas exhibition this week. Qasemi said he expected more than 1,000 foreign and domestic companies to attend.
The Organization of Petroleum Exporting Countries, in its April report, said Iranian crude oil production declined from 2.7 million barrels per day in January to 2.6 million bpd in March.