public limited partnership composed of corporate assets spun off (roll out) or private limited partnerships (roll up) with income, capital gains, and/or tax shelter orientations. Interests are represented by depositary receipts traded in secondary market . Investors thus enjoy liquidity . Flow-through tax benefits, previously possible within passive income restrictions, were limited by tax legislation passed in 1987 that would treat most MLPs as corporations after a grandfather clause expired in 1998.