The rates of Service Fees shall be described in Offer Sheets. Service Fees described in Offer Sheets should be all fees which DELTA pays. No additional charges (except such additional charges as are consented by DELTA) should be borne by DELTA. The parties acknowledge that the cost of providing certain services may be affected by external market forces beyond the control of either party. Therefore, CARRIER may propose reasonable pricing adjustments to reflect changes to: governmental or port charges; fuel or security surcharges; cargo screening fees; peak season; general rate increases, Acts of God; and/or changes in the market prices available to CARRIER. DELTA has the right to reject a pricing adjustment proposal provided that CARRIER has the right to suspend any services directly affected by the external market force. DELTA shall make payment within fifteen (15) calendar days from the date of invoice, excluding customs duty and tax obligations which shall be paid directly by DELTA.