Oil refinery S-Oil paid the highest average wages in Korea last year, according to a study by Job Korea published Tuesday. The employment portal surveyed 80 companies in the country's top 100.

S-Oil paid an average of W138 million to staff in 2018, up 14 percent from 2017, compared to the W82 million average for all companies surveyed (US$1=W1,137).

An S-Oil staffer said, "Due to the nature of the oil-processing industry, we have a relatively small number of staff, but they stay with the company for an unusually long average of 16 years." That means they get more raises.

Thirteen companies paid six-figure wages, and six of them were financial institutions, which top the employment wish list of jobseekers. They are Meritz Securities with W136 million, Samsung Securities (W122 million), NH Securities (W121 million), Samsung Fire and Marine Insurance (W100.7 million), Mirae Asset Daewoo (W100.6 million) and Samsung Card (W100.1 million).

In the semiconductor industry, which is also highly sought-after, Samsung Electronics topped the list with W102 million, ranking sixth overall, while SK Hynix ranked ninth with W100.7 million. Thanks to the chemical industry super cycle, Lotte Chemical (W100.6 million) also joined the ranks of top payers.

Others in the Top 20 were Netmarble (W93 million) and NCsoft (W89.5 million), while Kakao (W84.1 million) and Naver (W77.1 million) ranked within the Top 30 to 40. Kakao and Naver have a higher staff turnover of between four to five years, which pushes down the average salary.

Although more women joined the workforce, they were still underpaid compared to men. Their average salary stood at W58 million, way below that of men at W90 million.

Samsung Electronics paid the highest average wages to female workers at W93 million, followed by Samsung Securities with W92.7 million and S-Oil with W89.2 million.