Okx van Leeuwen: Tax Lawyers in Business! Okx van Leeuwen Tax Lawyers in Business provides tax advisory to both (international) companies and individuals. Okx van Leeuwen is ran by tax lawyers combining more than 25 years experience in the field of tax advisory. By handling all cases ourselves, and keeping our overhead costs low, we offer a professional, efficient and personal service to each of our clients at competitive rates. We are members of the Dutch association for academic tax lawyers (www.nob.net).