upon sth.在合同中，通常表示“一...就...”，相当于as soon as...，表示只要某情况出现或具备时，就会引起另一种情形的发生。有时还可以用on sth.或on doing sth.代替upon。

例：Upon the occurrence of any of the following events,this Agreement may be modified or rescinded as the Transferor and the Transferee may mutually agree. (出现下列情形之- -的， 本协议可经转让方和受让方协商一致而变更或撤销。)

Upon execution of this Agreement, the Ventures shall each own the following interests in the Venture. (本协议一经成立， 合资各方应享有企业的下列权益。)

Upon completion of lading, the Seller shall, within 3 days after shipment, send two sets of copies the documents listed in 3.4.3 above to the Buyer direct by express courier. (装船-经结束， 卖方应于装船后3日内通过特快专递直接向买方寄去上述第3.4.3条约定的单据。)