The biggest rush of borrowers this year descended on the bond market Wednesday as companies sought to lock in financing before the Federal Reserve considers raising interest rates for the first time in almost a decade.

Global optimism that buoyed equities from Japan to Europe fostered demand for company debt and cleared the way for benchmark-sized bond deals, including a $10 billion offering by Gilead Sciences Inc. and Frontier Communications Inc.'s plan to raise $6.6 billion– which would be the year's second-biggest junk offering.

Companies that have borrowed a record $1.2 trillion this year are taking advantage of renewed investor appetite and rock-bottom yields to close the loop on financing before a Fed rate hike makes it more expensive to sell debt. The flurry of deals today came after issuance froze for 13 consecutive days starting in August when concern about an economic slowdown in China crimped sales — exacerbating a lull during a period that's historically slow.