As the e-commerce sites are being more secure and reliable in recent years and the number of transactions is rising rapidly, parallelism can help us to reduce response time and increase throughput for e-commerce transactions. This paper will investigate parallelism in on-line transaction processing. It aims to specify those aspects of e-commerce transactions that would profit from parallel processing and analyze current parallel processing techniques to determine those which can be used for e-commerce transactions. The parallel processing techniques proposed in this paper can be easily applied to B2C and B2B on-line transaction processing. Although some parallel implementations of databases have been proposed, to the best of our knowledge, parallel implementations of on-line transaction processing specific to e-commerce are rarely existed.