<p>The worldwide distribution of the small degree-3 M1 ocean tide is investigated using a quasi-global data set of over 800 tide gauge records and a global tide model. M1 is confirmed to have a geographical variation in the Atlantic consistent with the suggestion of Platzman and Cartwright that M1 is generated in the ocean as a consequence of the spatial and temporal overlap of M1 in the tidal potential and one (or at least a small number) of diurnal ocean normal modes. As a consequence, it is particularly strong around the UK and on North Sea coasts. This analysis shows that their suggestion is also consistent to a great extent with the observed small amplitudes in the Pacific and Indian Oceans. However, there are differences at the regional and local level which require much further study via more sophisticated ocean tidal modelling. By contrast, the M1' tide is shown to have a geographical distribution consistent with expectations from other degree-2 diurnal tides, apart from locations such as around the UK where tidal interactions introduce complications. As far as we know, this is the first time that these small tidal constituents have been mapped on a global basis and, in particular, the first time that the ocean response to the degree-3 component of the tidal potential has been investigated globally.</p>