In this article we present a survey of routing methods in Optical Burst Switching (OBS) networks. We begin with a description of routing approaches and follow the discussion with a detailed classification of routing algorithms in OBS. Afterwards, we discuss common OBS network loss models that are frequently used in routing optimization. As examples of such application, we present a linear and a nonlinear formulation of a multi-path routing optimization problem with an indication on convenient resolution methods. Presented algorithms are appropriate for proactive load balancing routing and aim at the improvement of network-wide burst loss performance. To compare performance results, both methods are evaluated by simulation in a set of unified network scenarios.