My OB gave me a brochure put out by The Royal Australian & New Zealand College of Obstetricians & Gynaecologists and it lists ideals of weight gain as follows, based on your BMI pre-pregnancy.

BMI 18.5 or less (Underweight): 13-18kg weight gain
BMI 18.5-24.9 (Normal/Healthy): 11-16kg weight gain
BMI 25-29.9 (Overweight): 7-11kg weight gain
BMI 30-34.9 (Obese Class 1): 4-11kg weight gain
BMI 35.0-39.9 (Obese Class 2): 0-4kg weight gain
BMI 40 or more (Obese Class 3): 0kg Weight gain, LOSE up to 4kg

Hope this helps