In a medium bowl, whisk together the olive oil, ranch dressing, Worcestershire sauce, greek seasoning, salt, lemon juice, vinegar, pepper, and sugar.
Place chicken in the gallon size ziplock bag. Add marinade, push air out of the bag and seal. Refrigerate for at least 8 hours.
Heat the grill for medium-high heat. Grill chicken for 5-6 minutes per side, or until the chicken is no longer pink in the center and reaches 165° Fahrenheit (75° Celsius).
Remove from grill, rest for 2-3 minutes and serve.