OKLAHOMA CITY – The $1.3 billion Tinker Federal Credit Union saw its card portfolio increase in value by $3 million after the credit union employed a mixture of credit line increases, new account acquisitions, pre-approved upgrades and balance transfers, the credit union said. This spring, the credit union mailed more than 13,500 Visa Platinum upgrade letters that also included a 5.99% balance transfer offer until paid in full. More than 22% of recipients accepted the offer for a total gain in outstanding balances of $1.3 million. Balance transfers associated with this offer totaled $570,000. The credit union also mailed 32,400 pre-approval letters to non-cardholding members with an introductory rate of 2.99% for six months and launched a credit line increase for qualified cardholders late last year that boosted average monthly balances by almost 23% or an average of $166 a month per cardholder. Tinker is a member of PSCU Financial Services and used the cooperative's card resources to help achieve its goal.