They are all different although there are a few different models. You need to look at the prospectus to find out the details. It can be found on the SEC website. Actually WHX will end in one year from now. SDR is also a limited lifetime trusts. NDRO and ROYT on the other hand are perpetual trusts. That doesn't mean they last forever, rather it means the termination will occur when there is insufficient reseres left to continue economically rather than having a pre-defined termination criteria.