upon reciept vs once receipt

Some examples from the web:

• The merger is anticipated to close upon reciept of approval from the Small Business Administration, which is expected in the near future. Freshstart Venture  ...
• Evolution Motorsports Carbon Fiber Interior Kit Price Includes $1000 Core Charge. Refundable upon Reciept of "New" Condition Interior Parts wihen 30 Days.
• The registration is first confirmed and legally binding upon reciept of confirmation in writing per post from the Complexity Management Academy GmbH. To every ...
• Receipt of goods procedure and instructions in case of loss/damage. 1. Loss/ damage apparent upon reciept. Examine the goods immediately on delivery.

Some examples from the web:

• Return at once on receipt of this
• It is sent once after receipt of a "channel free" telegram
• On the day following its publication in the Official Journal of the Community of Valencia, once acknowledgement of receipt has been received from the Commission.
• Once acknowledgement of receipt by the Commission has been received, on the day following publication in the Diario Oficial de la Comunidad Valenciana (Official Gazette of Valencia)
• So once a week, according to these receipts?
• You'll be expected to hand over all receipts and unexpended cash... once your operation is complete.
• You'll be expected to hand over all receipts and unexpended cash... once your operation is complete.
• The decision to grant subsidy will be issued once the EU has confirmed receipt of this notification.
• You once told me how much you hated that your father measured his happiness by the night's receipts.
• Each undertaking in receipt of an authorisation shall be checked at least once per year.
• You know, I once tracked a Rothko to the Hamptons using a jitney receipt.
• Electronic receipts shall be sent at once to the vessel by both addressees, with a copy to the other.
• Once this principle has been established, it is up to the Commission to investigate on an individual basis any allegations according to which the nuclear sector is in receipt of subsidies engendering unfair competition.
• If this notification is sent by e-mail, electronic receipts shall be sent at once to the vessel by both addressees, with a copy to each other.
• Once the application has been registered, an acknowledgement of receipt shall be sent to the applicant, unless a reply is sent immediately.
• In practice acknowledgement of receipt is forwarded within the deadline specified by Article 14 of the code in respect of any request in the form of a petition once it has been duly registered.
• Once the observations are received, the Office will issue a receipt to the person making the observations (the 'observer'), and the observations will be communicated to the applicant.
• After receipt of the identification number issued by the Commission once the summary information has been received
• No further time limits for receipt of requests to participate shall apply once the invitation to tender for the first specific procurement under the dynamic purchasing system has been sent;
• Once the request for an opinion has been received, an acknowledgment of receipt is sent to the consulting authority in the same language as the consultation request.