Two leading opposition candidates for next month's Seoul mayoral by-election are double digits ahead of their ruling party rival should their unify candidacy and run in  two-way race, a survey showed Sunday.

Conducted by three pollsters, Ipsos, Korea Research and Hankook Research, the survey found that Oh Se-hoon of the main opposition people Power Party garnered 47 percent with Park Young-sun of the ruling Democratic Party winning 30.4 percent in a hypothetical two-way race.

Ahn Cheol-soo of the People's Party got 45.9 percent versus the ruling party candidate's 29.9 percent in a two-way contest, according to the survey commissioned by three broadcasters, SBS, KBS and MBC.

In terms of suitability for a unified opposition candidacy, Oh got 34.4 percent, just 0.1 percentage point more than Ahn. When it comes to competitiveness, Oh and Ahn received 39 percent and 37.3 percent, respectively.

In the case of the two candidates pitted against Park in a three-way race after their failure to unify candidacy, Oh, Park and Ahn got 30.2 percent, 27.3 percent and 24 percent, respectively.

For the Busan mayoral by-election, support for Park Hyung-jun, candidate of the People Power Party, was recorded at 38.5 percent, while Kim Young-choon of the ruling party received 26.7 percent.

The survey was conducted on Saturday and Sunday on 1,006 people in Seoul and 1,000 in Busan, who are aged 18 or older. The survey has a margin of error of plus or minus 3.1 percentage points with a 95 percent confidence level. (Yonhap)