In a shallow dish or bowl, mix together the flour, salt, pepper and oregano. Coat chicken pieces in flour mixture.
In a large frying pan, melt butter in the oil over medium heat. Place chicken in the pan, and lightly brown on one side. Turn over the chicken pieces, and add mushrooms. Pour in wine and sherry. Cover the pan; simmer chicken 10 minutes, turning once, until no longer pink and juices run clear.