A type of sinking fund bonds (sinkable bonds or sinkers) in which an equal percentage of bonds are redeemed from each bondholder at specific times prior to maturity. This bond is embedded with the so-called pro-rata sinking fund option, which allows the issuer to sink away “pro-rata” (usually across all maturities in an issue). Rather than determining which bonds to redeem or sink away by lottery, pro-rata sinkable bonds stipulate a flat percentage of bonds are spread among all current holders of the bond (investors).