According to the survey, about 30 percent of those polled were ready to support PSOE, which means the party will win 17 or 18 seats in the European parliament.
The centrist Citizens party received 14-16 percent of the vote, which would give it 8 to 9 seats. The leftist Podemos party received 12-15 percent of the vote, giving it 8 seats.
At the same time, at least 7-9 percent intend to vote in the EU elections for Spain's right-wing VOX party, which will mark the first time the nationalist party will have representation in the European parliament.
READ MORE: Voter Turnout in Spanish Parliamentary Elections Exceeds 60% — Interior Ministry
The poll was carried out throughout Spain between 21 March and 23 April with 17,641 adults responding. The margin of error is 0.75 percent.