Wall Street securities dealers and money managers are increasingly relying on algorithms to execute even the biggest corporate-bond trades, the latest sign of movement toward electronic trading in a $12 trillion market that was long one of the biggest holdouts.

Around 35% of block trades worth $5 million or more are now handled through RFQs, or electronic requests for quotes, and portfolio trades, which are mostly electronic, according to Barclays Plc’s analysis of data on the investment-grade market through the end of last year. That’s up from just 7% a little less than a decade ago.