Security firm G4S is planning on issuing bonds worth around 500 million euros, a source close to the situation said on Wednesday, adding that the maturity of the notes would be determined following a five-day roadshow ending next week.

Several banking sources had earlier told Thomson Reuters' IFR that the FTSE 100 firm, rated BBB by Standard & Poor's, had mandated Bank of America Merrill Lynch , Barclays , BNP Paribas and Danske Bank to arrange a series of meetings, starting on Friday, April 13, to gauge European investors' appetite.

The roadshow will start in Helsinki, before moving on to Copenhagen, London, Paris, Frankfurt, Munich and then wrapping up in Amsterdam next Thursday, April 19, bankers said.

A euro-denominated issue would make most sense since they already have a sterling bond out there, but no final decision will be taken until after the roadshow, the source said, adding that any deal would likely be benchmark-sized - or around half a billion.

G4S, which would not comment when contacted by Reuters, was last in the public bond market in May 2009 when it issued 350 million sterling of 10-year bonds, with a coupon of 7.75 percent, off the back of a euro medium-term note programme.

The proceeds from that transaction were used to repay debt outstanding at the time, in line with the group's strategy to reduce reliance on bank debt.

The notes priced at 410 basis points (bp) over the benchmark Gilt at the time, and were trading at around 250bp over that benchmark on Wednesday.

New deadlines for reaching minimum capital ratios have for months been getting European banks hot under the collar, making corporate lending far from a top priority and forcing companies to diversify towards bonds and away from loans.

Several syndicate bankers said that G4S would be doing just this with its upcoming bond issue.

G4S, which is the official security provider for the 2012 London Olympics, posted operating profit of 531 million pounds for 2011. In March it said it would focus on expanding in emerging markets like India, China and Brazil after a failed 5.2 billion pound takeover of Danish cleaning firm ISS last year.

Five-year CDS on G4S - which, however, is relatively illiquid - was trading at around 148.5bp on Wednesday according to Thomson Reuters data, compared to 92.74bp for peer Securitas AB , according to Markit.

CDS, or credit default swaps, are financial instruments used to insure against the default of debt issuers. They are expressed as a percentage of the amount of debt covered and a basis point equals 1,000 euros annually on a swap protecting 10 million euros of debt.

Shares in G4S were trading 2.75 percent higher by 1205 GMT, outperforming the FTSE 100 index which was up 0.6 percent.

(Editing by Helen Massy-Beresford)