Three methods for the estimation of directional spectrum, the Bayesian approach (BDM), the maximum entropy principle method (MEP) and the extended maximum likelihood method (EMLM), are applied to the analysis of the wave records acquired at an offshore oil rig 42km off the Iwaki coast (Northeastern coast of the main island of Japan), where four step type wave gauges and a two-axsis directional current meter with a pressure sensor are installed on the legs of the oil rig for ocean directional wave measurements.
　Firstly, the validity of the above mentioned methods when they are employed for various types of probe array is examined on the results from the field observation data. Secondly, some properties of the real directional random waves are discussed from the examples of the directional spectra estimated by the BDM.
　The major conclusions are as follows.
1) As the number of wave probes increases, the directional resolution shown by the BDM is improved, while such improvement is not clearly seen for the EMLM.
2) The MEP is recommended for a point measurement of only three elements, and the BDM is recommended when four or more wave probes are employed.