The online retailer, which is 40% owned by Waitrose, has been working with O&M since March 2004.
The review follows Ocado's decision to raise £60m to expand the geographic area in which it operates.
It has yet to show a pre-tax profit in the six years it has been running; sales for the year to 26 April were £126m, according to TNS.
Ocado, which delivers groceries from Waitrose supermarkets, currently covers about one-third of the country. It has been left behind by the major supermarkets, which have 80% coverage because they distribute via stores rather than a central warehouse.
Last year, the firm made its first foray into the North of England with a distribution centre in Manchester.
There has been speculation that Ocado will attempt to float on the stock market within the next 18 months.
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