He regularly represents clients in proceedings before competition and regulatory authorities and courts. Kees has extensive experience in cartel and merger control proceedings before the Dutch Competition Authority and the European Commission, including in the telecommunication and media sectors. He also advises and litigates on matters of EU law and private enforcement of competition law including cartel damages cases.

Kees regularly publishes on competition law and he is also an author for Tekst & Commentaar Mededingingsrecht.

The 2024 edition of Chambers Europe describes Kees as "In my view, he is really one of the top-notch competition specialists in the Netherlands, so we are really happy with him" and "He is pleasant to work with, and offers creative solutions and great commercial awareness".