Eurail and Reservations

Probably not. Most trains except for the locals now require reservations. But I am not that familiar with the Beneleux area so you need to look at schedules between the various and see how many trains have the little r for reservations required. And that will answer your question.

In Belgium and the Netherlands, only Thalys trains require reservations. They are possible, recommended, but not mandatory on the Deutsche Bahn ICE trains that service Brussels and Amsterdam to and from Germany. Reservations are not available for all trains operated by the two national rail companies, NMBS in Belgium and NS in the Netherlands. You buy a ticket, get on the next train, and find a seat. And don't buy a Eurail or Rail Europe pass for these two countries anyway. They will massively overcharge you, and the trains in these two countries are pretty cheap to begin with. NMBS sells it's own pass that is a bargain compared to all other third party sellers. I don' t have time to describe it now, but its available at all train stations in Belgium. The Netherlands has some "OV Chipkaart" (I think OV stands for "openbaare vervoer", which translates as "public transportation") system that sort of acts like a pass on all public transit, but I haven't figured out the details yet.

Good information guys, thanks a bunch!