Ferry tickets for the Mersing to Tioman ferry service are available here, here, here or here, as well as for walk-in travelers.
That being said, please note that by the time last-minute walk-ins arrive at the Mersing Harbour Centre ticket counter, the ferry may no longer have seats available, given that the vessel may be fully booked by then.
Tioman Ferry's service and follow-up is prompt and assuring. Apart from ferry tickets, their website also offers bus and hotel booking options. Their informative emails are to-the-point and contain all relevant information a visitor would need to plan his/her trip.
-- Andy --
Now, if you've already booked your Tioman hotel and resort and your dates are fixed, it clearly makes quite a bit of sense to ensure you have ferry tickets for your booked hotel dates by booking your inbound and outbound ferry tickets online, i.e. before leaving Singapore.
Additionally, it should be noted that ferry crossing frequency on any given day is subject to the tidal range for that day. This means that on certain days the number of crossings to Tioman and back to Mersing - and by extension, the number of available seats - may be limited.
Have an enquiry about ferry tickets to Tioman? Send it here...