So a perpetual bond has both major advantages and disadvantages. The advantage is liquidity - all the different issuances are interchangeable like common stock,

So a perpetual bond has both major advantages and disadvantages. The advantage is liquidity - all the different issuances are interchangeable like common stock, so instead of N different markets for each of N times the company raised money via selling bonds, there's one market. The disadvantage is that bonds do not just entitle you to periodic coupon payments, but also give you rights according to the face value of the bond in bankruptcy proceedings. Selling bonds far from the "par" you are theoretically owed in bankruptcy has big problems - either the bond is trading above par and you risk not being made "whole", or it is below par and the company is selling bankruptcy liabilities on their assets for pennies on the dollar. The movement of interest rates over time guarantees that one of these situations will eventually hold, so either issuers or buyers will want to adjust the nominal yield (and thus par value), resulting in the loss of interchangeability. Notably, the US government has zero risk of being able to pay its nominal obligations, so is a prime candidate for issuing perpetuals in a way that corporations cannot. Currently, if you buy a new 20-year treasury bond and wait 2 years, you end up with an off-the-run bond that is difficult to efficiently trade. It'd be much better if these instruments did not "expire" as such, and the increased usefulness to investors would wind up reflected in lower financing costs for the government. Theoretically, the entire US treasury bond structure could be replaced with a zero-duration overnight interest account, a perpetual that pays a $1 coupon per day, and an inflation-linked perpetual that pays the CPI as coupon.