Bond sales worldwide are reviving from the slowest month of the year as yields on corporate debt decline to the least since 2010.

GlaxoSmithKline Plc's $5 billion offering, its first dollar-denominated sale in more than four years, led issuance of at least $55.1 billion this week following $45.8 billion in the period ended April 27, according to data compiled by Bloomberg. Stockholm-based Ericsson AB, the biggest maker of mobile phone networks, sold $1 billion of 10-year bonds to refinance existing debt, its first issue in almost three years.

Borrowing costs are declining as investor demand rises amid optimism that the global economy isn't slowing enough to dent corporate creditworthiness. Some 71 percent of U.S. companies that have reported first-quarter earnings beat analysts' estimates, data compiled by Bloomberg show. Mutual fund inflows for fixed-income funds globally rose last week to the highest level since March, according to research firm EPFR Global.