To define the different levels of third-party logistics, a stage or
level model can be used. A few of these have been put forward earlier. Halldorsson and
Skjoett-Larsen (2004) have proposed a model with four different steps: market
exchanges, customized logistics solutions, joint logistics solutions, and in-house
logistics solutions. This stage model indicates three different levels of outsourced
services, and one of these is market exchanges.