For the first time since they moved into their sparkling bayfront ballpark nearly two decades ago, the Giants are lowering season-ticket prices on a widespread scale — and offering other fan-friendly inducements in response to declining attendance.

Ticket holders learned of the program by email Wednesday. In addition to reducing the cost of 80% of season tickets for the 2020 season, the Giants are offering a “signing bonus” for customers who renew by Oct. 10; allowing fans to roll tickets for up to eight games into 2021; and changing their parking plan to permit existing customers to choose specific games rather than pay for the full home schedule.

The amount of the ticket-price reduction varies based on the location of seats, but Russ Stanley, senior vice president of ticket sales and services, said it will be as high as 21% in the “view infield” section and the back rows of the bleachers.

“It’s a pretty big change,” Stanley said Thursday in an interview with The Chronicle.

Another 15% of ticket prices at Oracle Park will remain unchanged for the ’20 season, meaning the Giants will not raise prices on 95% of their seats. They will boost prices on the remaining 5%, mostly for prime spots behind home plate.

This broad reduction comes with the Giants on the verge of missing the playoffs for the third consecutive season. Their average attendance of 33,550 marks a 13.9% drop from last season, when the average was 38,965, and a 19.5% drop from 2015 (average: 41,678).

“The impetus was focus groups and our experience with season-ticket holders this year,” Stanley said. “I’d like to think the Giants are listening; we want to provide the best experience for our fans.

“What we heard is there’s softness in the secondary market, so we’re helping with pricing. We’re hearing, ‘I can’t go to 81 games,’ so there’s an exchange program. … I’m excited. We’ve had a pretty good response from our season-ticket holders.”

One of those people, Marianne Biskup of Scotts Valley, was leaning toward dropping her tickets until this week’s news. Biskup has had two season tickets since 1999, the Giants’ final year at Candlestick Park, but the difficulty in unloading unneeded tickets — and the team’s struggles on the field — gave her pause.

Then came word of the reduction in prices, which could total $1,100 in all (about 20% of her total cost) for Biskup’s two seats in “view reserved,” behind home plate.

“I was 90% sure I wasn’t going to renew,” she said. “We were hemorrhaging cash for a couple seasons, and that’s a lot of money to lose. Now I’m definitely leaning the other way. Saving $1,100 is a big incentive.”

Biskup, like many fans, has historically re-sold tickets for some games on the secondary market. This worked in the Giants’ glory days, when they won three World Series titles in five seasons, but that market “dropped off the cliff” in the past year or two, as Biskup put it.

Another longtime season-ticket holder, Chard Nelson of Oakland, will save less than 4% on his two tickets under the revised pricing structure. But Nelson, who attends 30 to 40 games per season, welcomed any changes to help him recoup some of his investment.

“I used to throw tickets on Stub Hub and come close to getting what I paid,” Nelson said. “The last two or 2½ years, that just vanished. Either you can’t sell them at all, or so many others are selling them for a pittance, it’s not even worth it. That market just dried up.”

The Giants sold 26,000 full season-ticket plans this season, according to Stanley, down from a high point of 30,000 in 2016, the last time the team reached the postseason.

Overall, the Giants are on pace to draw slightly more than 2.7 million fans this season, the first time since 2009 they will not crack the 3 million mark. They drew more than 3.3 million for eight consecutive years, from 2010 through ’17 — highlighted by a National League-record sellout streak of 555 home dates, including the postseason — before dropping to 3.16 million last season.

The Giants ranked among the top three in National League attendance in each of the past eight years. They’re seventh so far this season.

“It’s hard to go at 8,000 rpms every year,” Stanley said. “We’re redlining on attendance. We’ve sort of come back to earth a bit.

“We put a lot of faith in primary and secondary market data, and we have a whole analytics team here. The numbers were telling us we probably needed to make some adjustments.”

Season-ticket holders who renew their plans by Oct. 10 essentially will receive a credit of $250 per club level seat and $100 per seat elsewhere in the ballpark.

Some fans spoke on Twitter of the club’s plans to build a bar area in the left-field seats, which would reduce seating capacity. Stanley said nothing is official, as the Giants contemplate possible locations for a social/destination area similar to what they currently offer beyond the center-field bleachers.

Clearly, the team is seeking creative ways to maintain its fan base amid a rebuilding project on the field.

“Our fans are passionate,” Stanley said. “They still want to come to games, they’re just not coming to as many games. Instead of 80 games, they may come to 60 or 70.”

Ron Kroichick is a San Francisco Chronicle staff writer. Email: rkroichick@sfchronicle.com Twitter: @ronkroichick