The following table sets forth the aggregate contractual cash obligations as of December 31, 2001 (in thousands): Titan has never entered into any off-balance sheet financing arrangements and has never established any special purpose entities. We have not guaranteed any debt or commitments of other entities or entered into any options on non-financial assets. The only transactions between Titan and related parties during 2001 were a loan made to an officer and an agreement with certain of our officers and directors to rescind stock options that were previously granted and exercised. We expect to continue to incur substantial additional operating losses from costs related to continuation and expansion of product and technology development, clinical trials, and administrative activities. We believe that we currently have sufficient working  capital to sustain our planned operations through 2005. Our portfolio of marketable securities creates an exposure to interest rate risk. We adhere to an investment policy that requires  us to limit amounts invested in securities based on maturity, type of instrument, investment grade and issuer. We satisfy liquidity requirements by investing excess cash in securities with different maturities to match projected cash needs and limit concentration of credit risk by diversifying our investments among a variety of high credit-quality issuers. We do not use derivative financial  instruments in our investment portfolio. The following table summarizes principal amounts and related weighted-average interest rates by year of maturity on our  interest-bearing investment portfolio at December 31, 2001 (in thousands, except interest rate): Quantitative and Qualitative Disclosures About Market Risk Face Value Estimated 2002 2003 2004 2005 2006 Total Fair Value Cash equivalents and  marketable securities Variable rate securities $ 5,478 — — — — $ 5,478 $ 5,478 Average interest rate 2.640% — — — — 2.640% Fixed rate securities $41,468 $53,341 — — — $94,809 $99,279 Average interest rate 6.610% 5.601% — — — 6.043% Payments Due by Period Total <1 year 2-3 years 4-5 years 5 years+ Contractual obligations Operating leases $3,246 $ 669 $1,433 $1,144 — Sponsored research and license agreements $3,243 $1,596 $ 659 $ 659 $329 Total contractual cash obligations $6,489 $2,265 $2,092 $1,803 $329 Seventeen