He competed in Polish Team Chess Championship many times, winning three bronze medals in 2013, 2016 and 2017 (also in the colors of Polonia Wrocław).

[2] Oskar Wieczorek met the norms for the title of Grandmaster at Polish Team Chess Championship (2016),[3] in Legnica (2018)[4] and on the German 2.

[5] In 2008, Oskar Wieczorek shared 2nd place (with, among others, Łukasz Cyborowski) in the open chess tournament in Rewal.

In 2016, he shared second place (behind Andrey Vovk) in the tournament 5° Open Internazionale del Salento - A in Gallipoli.

[13] Oskar Wieczorek achieved the highest rating in his career so far on May 1, 2022, with a score of 2505 points, he was ranked 26th among Polish chess players.